1. Field of the Invention
The present invention relates to a method of forming a lead frame for use in the fabrication of a semiconductor device.
2. Description of the Prior Art
A semiconductor device such as an IC or an LSI is fabricated by mounting a semiconductor integrated circuit on a pad 1 of a lead frame as shown in FIG. 1, interconnecting terminals of the semiconductor integrated circuit to inner leads 2 of the lead frame by means of a gold or aluminum wire bonding process and further sealing the resultant integrated circuit with resin or ceramic.
In FIG. 1, reference numeral 3 is an outer lead, 4 and 5 are side rails, 6a and 6b are tie bars (dam bars), and 7 is a support bar.
There are conventionally two methods of forming such a lead frame, namely, by etching and by pressing using a lead frame blanking die.
The former method is suitable for the fine processing of the tip ends of the inner leads 2, while it is disadvantageous in that the production cost is high because deteriorated etching solution must be continuously or periodically exchanged.
On the other hand, the latter method is advantageous in that the production costs can be rendered low, but is disadvantageous in that when fine processing is desired, a very small blanket chip raised together with a punch during the upward movement of a press may cause damage to the die and it is rather difficult to make such a die, and in addition the product accuracy is inferior as compared to that made according to the former forming method.